Cardiovascular hypertension has been induced in rats by administration of the oral contraceptive, Enovid. The projects described here are designed to assess further use of the rat as an experimental model for the production of hypertension by means of oral contraceptives. An attempt will be made to determine: (a) the effect of estrogen versus progestogen in the development of hypertension in rats; (b) the reversibiliiy of the effect of an oral contraceptive on blood pressure; (c) the effect of an oral contraceptive on the rate of development of genetic (spontaneous) hypertension; (d) the effect of age on elevation of blood pressure in rats receiving an oral contraceptive; (e) the effect of an oral contraceptive on the metabolic and pressor responses to administration of alpha and beta adrenergic agents; and (f) the effect of acute and chronic administration of an oral contraceptive on sodium and potassium exchange.